Butterworth Filter

Use the Butterworth option to apply a Fast-Fourier Transform Butterworth filter to a channel.

The filter option is available with the following extensions and menus:

• Geophysics: 1D FFT > 1D Filtering
• Gravity and Terrain Correction: Moving Platform Gravity  > Apply Single FFT Filter

Butterworth filter options

Central Wavelength cutoff (in ground units)	Central Wavelength cutoff value, in ground units (Default 1) Script Parameter: FFTBUTTW.WAVEL
Degree of Filter	Degree of the Filter function (default = 8) Script Parameter: FFTBUTTW.DEGREE
Low or High Pass Filter	Low or High Pass filter (default = Low) Script Parameter: FFTBUTTW.PASS

Application Notes

The Butterworth filter is excellent for applying straight forward high-pass and low-pass filters to data because you can easily control the degree of filter roll-off while leaving the central wavenumber fixed. If ringing is observed, the degree can be reduced until acceptable. A common, but more complicated alternative is the Cosine Filter).

Butterworth Filter

Parameters:

k0	Central wavenumber of the filter.
n	Degree of the Butterworth filter function. By default, we assume a degree of 8.
0/1	Residual/Regional flag to specify if a residual high pass or a regional low pass is required. By default, the system applies a regional filter.